//: concurrency/SerialNumberChecker.java
// Operations that may seem safe are not,
// when threads are present.
// {Args: 4}
package concurrency;

import java.util.concurrent.*;

// Reuses storage so we don't run out of memory:
class CircularSet
{
    private int[] array;
    
    private int len;
    
    private int index = 0;
    
    public CircularSet(int size)
    {
        array = new int[size];
        len = size;
        // Initialize to a value not produced
        // by the SerialNumberGenerator:
        for (int i = 0; i < size; i++)
            array[i] = -1;
    }
    
    public synchronized void add(int i)
    {
        array[index] = i;
        // Wrap index and write over old elements:
        index = ++index % len;
    }
    
    public synchronized boolean contains(int val)
    {
        for (int i = 0; i < len; i++)
            if (array[i] == val)
                return true;
        return false;
    }
}

public class SerialNumberChecker
{
    private static final int SIZE = 10;
    
    private static CircularSet serials = new CircularSet(1000);
    
    private static ExecutorService exec = Executors.newCachedThreadPool();
    
    static class SerialChecker implements Runnable
    {
        public void run()
        {
            while (true)
            {
                int serial = SerialNumberGenerator.nextSerialNumber();
                if (serials.contains(serial))
                {
                    System.out.println("Duplicate: " + serial);
                    System.exit(0);
                }
                serials.add(serial);
            }
        }
    }
    
    public static void main(String[] args)
        throws Exception
    {
        for (int i = 0; i < SIZE; i++)
            exec.execute(new SerialChecker());
        // Stop after n seconds if there's an argument:
        if (args.length > 0)
        {
            TimeUnit.SECONDS.sleep(new Integer(args[0]));
            System.out.println("No duplicates detected");
            System.exit(0);
        }
    }
} /*
   * Output: (Sample) Duplicate: 8468656
   */// :~
